Digital wideband architectures are being increasingly utilized for high speed digital communications. Wideband generally refers to bandwidths from kilohertz to multi-gigahertz bandwidths. When the bandwidths of the signals being considered are larger than (e.g., a multiple of) the speed of the digital logic processing those signals, channelized architectures are used to accommodate the high bandwidth signals in a slower circuit. A direct digital synthesizer (DDS) is a type of frequency synthesizer that creates arbitrary waveforms from a fixed-frequency reference clock. A DDS uses a digitally deterministic frequency synthesis technique, which is based on a digital definition of the result to generate a signal, by using logic and memory to digitally construct the output signal, and a data conversion device to convert the signal from digital to analog domain. That is, the DDS method of constructing a signal uses digital principles, and the precise amplitude, frequency, and phase may be known and controlled.
Analog voltage controlled oscillators have been typically used to create waveforms, resulting in a limited frequency range. In digital architectures, the current practice involves direct digital synthesis where multiple parallel DDS circuits create I/Q at very high rates directly for bandwidths at speeds that are multiples of the digital logic. In other typical methods, each technique, defined as a waveform with a specific instantiation of frequency, phase, and amplitude parameters as a function of time, has to be aware of the channelized structure explicitly switch channels in the architecture or have a specific parameter selecting a channel. Each technique typically has a DDS associated with it and raw I/Q data are passed around data lanes.
Channelized radio receivers divide an incoming radio frequency signal into plural frequency-segregated segments for performing differing signal processing of the output signal in different channels, the physical separation of hardware relating to different channels, reduction of data rate per channel, and the preclusion of cross channel interference effects, among others. However, in such typical channelization techniques, a frequency and a channel must be calculated and specified for each signal, which adds complexity, particularly when summing signals together. Many attempts have been made at the wideband receive side of channelized architectures. There have also been architectures for the transmit side of narrow band radio waveforms, such as for communications. However, little work has been shown for wide band channelized transmit architectures.
Furthermore, waveforms (techniques) are often difficult to port between platforms due to platform dependent architectures. Usually a great deal of verification such as extensive testing on a simulator is necessary to verify the revised waveforms to be ported to a new platform. Most existing waveform generators are platform dependent and have to be modified to fit a certain channelization scheme or parallelization scheme. Many attempts have been made to write portable. The main set of attempts has been targeted at writing C code or other general purpose code. However, the problem with C code (and most other coding languages) is that these languages are not portable to field programmable gate arrays (FPGAs) and other programmable logic devices and thus is not applicable to many of FPGA-based platforms.
These problems become aggregated and even more challenging in a wide band channelized architecture that needs to be portable to different platforms.